Note: Descriptions are shown in the official language in which they were submitted.
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Method and System for Determining Properties in a Vessel
The present invention relates to a method and a system for de-
termining properties of tissue or a fluid in a vessel according
to the preamble of the independent claims.
It is known in the prior art to treat vessels in a minimally in-
vasive way. For example, implants can be delivered using a cath-
eter device. Such treatments are used e.g. to treat constricted
vessels or aneurysms, amongst other conditions. Similarly, mi-
crorobots have been used in the prior art to image and/or treat
inner parts of a patient's body.
However, a problem that consistently occurs with such devices in
both treatments and diagnostic applications is that accurate in-
formation about the surrounding of the device is unavailable.
In particular, imaging techniques used in combination with mini-
mally invasive treatments typically only provide limited infor-
mation about the properties of the surrounding tissue. For exam-
ple, contrast imaging using X-rays provides anatomic information
of the vascular system, but may not be able to provide infor-
mation on mechanical properties or flow hindrances in the blood
stream. Thus, multiple methods are usually necessary in paral-
lel, making the collection of such information slow, costly, and
difficult. It is particularly difficult to obtain such infor-
mation in real time during a treatment with a minimally invasive
method.
Thus, the object of the present invention is to overcome the
drawbacks of the prior art, in particular to provide a method
and a system which allow to determine different properties of
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tissue or a fluid in a vessel neighbouring a device for treat-
ment or diagnosis of a human body in a simple way.
This and other objects are achieved by the method and the sys-
tems according to the characterizing portion of the independent
claims of the invention.
The invention relates to a system for determining properties in
a vessel or the heart (V) of a patient. The system comprises an
element to be placed in a vessel or the heart. The system fur-
ther comprises means for determining a propulsion force acting
on the element, and means for determining at least one of accel-
eration and velocity of the element. Preferably, the system com-
prises means for determining both acceleration and velocity of
the element.
Such means may in particular comprise a sensor, for example an
accelerometer, or a sensor adapted to measure a distance to a
reference point inside or outside the patient's body. Addition-
ally or alternatively, the means for determining a propulsion
force may also comprise an imaging device and/or a computer to
analyse images generated by the imaging device.
Furthermore, the system comprises means for determining at least
one property of a neighbouring medium of the element based on
the propulsion force, and at least one of acceleration and ve-
locity. For example, such means may comprise a computer, prefer-
ably a computer running a software code. Preferably, the means
determine at least one property based on both acceleration and
velocity of the element.
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The method according to the invention provides a way of deter-
mining properties in a vessel of a patient. It comprises the
steps of:
- Placing an element in a vessel or the heart
- Determining a propulsion force acting on the element.
- Determining at least one of an effective acceleration and
effective velocity, in particular both effective accelera-
tion and effective velocity, of the element,
- Determining at least one property of a neighbouring medium
of the element based on the propulsion force and the at
least one of effective acceleration and effective velocity
of the element, in particular both of the effective accel-
eration and effective velocity of the element.
The properties of the vessel that can be determined with the
method described herein can be mechanical properties, for exam-
ple the elasticity, stiffness, ductility, and/or hardness of a
tissue. By deduction, it would also be possible to determine an-
atomical or histological properties of the tissue, in particular
the presence of necrotic or cancerous tissue. Of course, it may
also be possible to determine physical properties of blood, such
as the viscosity and/or flow speed. Additionally or alternative-
ly, the properties can include properties of the vessel influ-
encing the flow, for example obstacles that prevent, slow down
or accelerate the flow of blood in the vessel or create turbu-
lences. It is also conceivable that other diagnostically rele-
vant properties are obtained, such as the presence of an aneu-
rysm, a blood clot/thrombus, gas bubbles, and/ or a defect in a
vessel wall.
A neighbouring medium shall in particular be understood as all
biological material in the vicinity of the element that can in-
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teract with the element. It can be liquid, solid, gaseous, or
comprise a soft material.
An element shall be understood as any device that is adapted to
move, at least temporarily, freely inside the human body. It
may, in particular, be a microrobot, a sensor, a drug carrier,
or a floating element. In particular, the element may comprise a
magnetic element, such as a ferromagnetic particle on its inside
and/or its surface. It may also consist of a ferromagnetic mate-
rial.
In particular, the method may be employed only to analyse prop-
erties of a vessel. Specifically, the method can be performed
for the sole purpose of determining a certain property of inter-
est. As such, the element is only introduced to, and does not
serve another purpose than, provide data to perform the method.
Additionally or alternatively, however, it is possible to per-
form the method with a medical device that is introduced in the
body to perform another action as well. For example, a micro-
robot may be introduced into the body to deliver a drug or treat
a target site. The method may then be performed to determine
when the microrobot has reached the target site, or even to de-
fine the optimal target site.
It would also be conceivable to use a separate element to per-
form the method in parallel to another treatment.
A propulsion force shall typically and unless otherwise stated
be understood as the total force that is exerted on the element
in the absence of any interaction with the patient's body. For
example, if the element is magnetic and is actuated by a magnet-
ic field, the propulsion force is the force that is exerted on
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the element by the magnetic field without taking into account
blood flow or other forces due to bodily functions, such as
friction in the body, blood flow, or blockage from a blood clot.
Similarly, if the element comprises a self-propelling means such
5 as a propeller or a jet, the propulsion force would be the force
exerted by this self-propelling means. If a combination of a
self-propelling means and a magnetic field is used, the propul-
sion force would include both those forces. It is possible to
calculate the theoretical acceleration and velocity from the
propulsion force for a given mass of the element.
The effective and theoretical acceleration and velocity will
never be the same due to influences such as friction, gravity,
drag, and others. In more sophisticated models, such effects may
be taken into account.
For example, if some parameters of the tissue or fluid neigh-
bouring the device are known, they are taken into account to
calculate a theoretical acceleration or terminal velocity that
the element should reach in that tissue based on the propulsion
force. For example, if the speed-dependent drag force that the
blood exerts on the element is known, the theoretical terminal
velocity of the element could be calculated.
By contrast, the effective acceleration and/or effective veloci-
ty of the element shall be understood as actual acceleration
and/or actual velocity of the element with respect to the pa-
tient's body. As such, the difference between the effective ac-
celeration or velocity and the theoretical acceleration or ve-
locity (which can be determined by division of the propulsion
force with the mass of the element) provides information on the
environment of the element (for example viscosity of the blood)
or obstacles.
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Consequently, the effective propulsion force shall be understood
as the product of the effective acceleration and the mass of the
element. For a given element, the effective acceleration is thus
an equivalent parameter to the effective propulsion force.
The propulsion force can be measured or determined based on
known parameters such as the parameters of an actuator such as a
magnetic field acting on the element.
Preferably, the propulsion force is determined based on a sensor
comprised in the element. This is particularly advantageous if
the exact location of the element is not known or difficult to
determine. For example, if the element is located in a large
vessel and driven by a magnetic field, the exact properties of
the magnetic field at the location of the element may not be
known. Thus, if the force exerted on the element by the magnetic
field can be measured, this problem is solved.
Additionally or alternatively, it is also conceivable to use an-
other sensor comprised in the element to measure the effective
acceleration.
Preferably, the method further comprises the step of imaging an
area of a patient where the element is located. In particular,
the imaging may be performed using one of X-ray imaging, magnet-
ic resonance imaging (MRI), computer tomography, positron emis-
sion tomography (PET), and ultrasound imaging. This can offer
several advantages in performing the method. On one hand, if a
certain mechanical property is determined by means of the meth-
od, imaging data can assist in the correct localisation and in-
terpretation (for example assignment to a certain type of tis-
sue). One the other hand, it is also conceivable to measure the
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effective acceleration and/or velocity of the element using the
imaging data.
Alternatively or additionally, it is also conceivable to use a
database of patients for calibration and interpretation of the
data for navigation the element or of data gathered by the meth-
od according to the invention. In such a database, information
about typical patients or groups of patients but also patient
individual information might be stored. Calibration and inter-
pretation may also be made by using artificial intelligence
methods. In particular, certain information usable for calibra-
tion or interpretation may be gathered by deep learning or ma-
chine learning methods. Such methods can be carried out during
the method according to the invention and/or in preparation
thereof.
Alternatively or additionally, it is also conceivable to use da-
ta generated by using a first element to modify parameters (e.g.
magnetic field) relevant for the navigation for a subsequent el-
ement.
Preferably, at least one property of the neighbouring medium is
additionally based on the imaging data. For example, imaging da-
ta can provide the information whether a certain number of dif-
ferent types of tissue are present. Additionally or alternative-
ly, imaging data may reveal the presence of an obstacle in a
vessel. Thus, one property of the neighbouring medium of the el-
ement is based on the imaging data, while other properties such
as the mechanical properties of the different tissue types or
the obstacle. The combination of the imaging data and the me-
chanical property may allow to conclusively determine what types
of tissue are present, and/or what kind of obstacle is in the
vessel.
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The person skilled in the art will understand that this is mere-
ly a non-limiting example of how imaging data can advantageously
be used in the method according to the invention. However, it is
possible to perform the method without imaging data.
Preferably, the method further comprises the step of determining
the location of the element. This provides additional infor-
mation of where certain tissue types are located in the pa-
tient's body. This is particularly advantageous in cases where
those tissues are planned to be treated or removed, for example
by a surgical technique.
Preferably, the location is determined by means of the imaging
technique.
Preferably, the method further comprises a step of saving in a
memory the at least one property of the neighbouring medium as a
function of the location or time. This allows for analysing mul-
tiple locations in a vessel during one session. In particular,
the data can subsequently be analysed such as to create one-,
two-, or three-dimensional property maps. For example, the ste-
nosis or an aneurysm of a vessel may be determined by means of
the method according to invention along the longitudinal axis of
said vessel. If the level of stenosis or aneurysm is determined
and saved at multiple points, a graph showing the stenosis or
aneurysm along the longitudinal axis can be obtained. Similarly,
data may also be collected in two or three dimensions.
Preferably, the step of calculating the at least one property of
the neighbouring medium is performed by a computer running a
software code. This allows for, in particular, automatically
performing the method and is thus fast, reliable and cheap.
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Preferably, the at least one property of the neighbouring medium
is one of mechanical, hemodynamical, anatomical, and histologi-
cal property. For example, it may be the viscosity of blood,
Young's modulus of a tissue, the flow velocity of blood, and/or
the size or shape of a vessel, in particular its diameter.
Preferably, the element placed in the vessel comprises a magnet-
ic element and the step of determining the propulsion force com-
prises determining the field strength of a magnetic field. De-
termining the field strength shall, in particular encompass the
calculation of the properties of the magnetic field at a certain
point in space (especially at the location of the element) based
on known parameters of a unit generating the magnetic field, but
can also comprise measuring the magnetic field at a certain
point in space. The measurement of the magnetic field may take
place by the element and thus at its location and/or at a refer-
ence point.
Preferably, the method further comprises the step of calculating
a theoretical acceleration or velocity of the element based on
the propulsion force acting on the element.
Preferably, the step of calculating a theoretical value of ve-
locity and acceleration of the element is additionally based on
the location of the element and imaging data acquired in the im-
aging step. For example, the size and blood volume of a vessel
may be taken into consideration based on imaging data. Addition-
ally or alternatively, the velocity and pulsatility of the blood
flow may be measured and taken into account, in particular by
means of Doppler ultrasound imaging. In particular, the location
of the element with respect to the vessel wall may also be taken
into account.
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Preferably, the method further comprises the step of measuring
the flow velocity of a liquid, in particular of blood in a ves-
sel or the heart, surrounding the element. Additionally the de-
termination of the at least one property of the neighbouring me-
5 dium may be based on the flow velocity. In particular, the flow
velocity may be determined by means of Doppler ultrasound imag-
ing. However, it is also conceivable to measure the flow veloci-
ty with a sensor comprised in and/or on the element.
10 Preferably, the method further comprises the step of localizing
the element by means of at least one detector and/or marker. The
marker can be placed on the element and the detector can be
placed at a pre-defined location in or with respect to the pa-
tient's body. For example, detectors may be placed on the out-
side of a vessel, on bones such as the skull, or organs such as
the heart. Detectors shall be understood as any device adapted
to detect or help to detect an element in its vicinity. Markers
are associated with the element and help to detect the element,
in particular by a sensor.
Detectors may also be adapted to measure the distance to an ele-
ment. A detector may particularly preferably be an electric sen-
sor, a magnetic sensor or an optical sensor. The markers could
be NFC chips, magnets or radiopaque material. Fluorescent or
isotopic markers may also be used.
The invention is further directed to a computer program product
for analysing the neighbouring medium of an element in a pa-
tient's body. It comprises a software code that is adapted to,
when run on a computer, perform the step of determining at least
one property of a neighbouring medium of the element based on
the propulsion force and the at least one of effective accelera-
tion and effective velocity of the element, in particular both
of the effective acceleration and effective velocity of the ele-
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ment. The computer program product may in particular be adapted
to process imaging data and preferably determine the at least
one property of the neighbouring medium based on imaging data of
the neighbouring medium acquired by an imaging device. For exam-
ple, the computer program product may be adapted to determine at
least one of velocity and acceleration of an element based on
imaging data.
The invention is further directed to a system for determining
properties of a vessel. It comprises an element adapted to be
carried by and/or actively move in a bodily fluid, a measurement
unit, and a calculating unit. The measurement unit is adapted to
determine at least one of acceleration and velocity of the ele-
ment. The calculating unit is adapted to determine at least one
property of the vessel based on the at least one of acceleration
and velocity of the element. Preferably, at least one of the
measurement unit and the calculating unit is adapted to deter-
mine a propulsion force acting on the element. For example, the
calculating may calculate the propulsion force based on on oper-
ating parameter, for example the characteristics of a magnetic
field. Additionally or alternatively, the measurement unit may
also be adapted to measure a force being exerted on the element,
for example by measuring a magnetic field. In particular, the
calculating unit may determine the at least property of the ves-
sel by performing a method as described herein, particularly
preferably by running a software code that is adapted to perform
the steps of a method as described herein.
The person skilled in the art will understand that the system
may, in particular, be adapted to perform any of the method
steps as described herein.
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Preferably, the system comprises an imaging device that is
adapted to image an area of a patient's body where the element
is located. This, in particular, allows for performing all steps
as described in the context of the method according to the in-
vention where an imaging unit can be employed. In particular,
the imaging unit may be any one of PET, MRI, ultrasound, X-ray,
and CT.
In the following, the invention is described in detail with ref-
erence to the following figures, showing:
Fig. 1: schematically an element in a vessel.
Fig. 2: schematically an element with different forces acting
on it.
Fig. 3: schematically an element in a narrowing vessel.
Fig. 4: schematically an element in a vessel and imaging devic-
es.
Fig. 5: schematically markers located on a vessel.
Fig. 6: schematically an element in a vessel with a blood clot.
Fig. 7: schematically a system according to the invention.
Fig. 8: schematically a magnetic element.
Fig. 1 shows schematically an element 1 in a vessel V. Here, the
element 1 is a moving element comprising a ferromagnetic materi-
al. Thus, a magnetic field applied by an external magnet (not
shown, see Fig. 8) may guide and/or propel the element 1 inside
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the vessel V. Thus, it can exert force 2 on the element 1. In
this case, in the hypothetical absence of influences e.g. by
bodily functions such as blood flow, friction, or gravity, the
exerted force 2 by the magnetic field would be the only force
acting on the element 1. It thus represents the propulsion force
in this example. However, due to fluid resistance, the element
is also subject to a drag force. Here, the drag force is unknown
and shall be determined in order to determine the fluid proper-
ties of blood and the friction on a vessel wall. However, it
would also be possible to include fluid resistance and friction
in the propulsion force. It is also possible to measure the ef-
fective acceleration 3 or velocity 4 of the element. Here, the
acceleration 3 is e.g. measured by an accelerometer comprised in
the element. Alternatively, it may for example also be measured
by means of an imaging device. The effective acceleration 3 rep-
resents the difference between the force 2 and the drag force.
Thus, it is possible to calculate the drag force and consequent-
ly also fluid properties of the blood and the vessel. This is
particularly advantageous, of course, where the flow properties
of the blood are affected by a condition.
Fig. 2 schematically represents a similar element as shown in
Fig. 1. Here, the vessel V is not shown for clarity. In addi-
tion, the element has a different shape and has a cubic instead
of a quasi-spherical shape. However, it also comprises a ferro-
magnetic material and can be propelled by a magnetic field. The
state schematically shown in Fig. 2 represents an equilibrium
state when the element has reached a terminal velocity 4. Hence,
the propulsion force 2 and the drag force 5 have equal norm val-
ues but opposite signs. The terminal velocity 4 can thus be used
to calculate parameters of the blood such as its viscosity. In a
similar embodiment of the method, the magnetic field may change
its direction with a certain frequency. Instead of measuring the
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velocity, one may measure the frequency of motion of the element
and determine fluid properties of the blood from that.
Fig. 3 shows schematically a different type of element 1. It is
spherical and is passively carried by a fluid in the vessel V.
It further comprises a sensor that is adapted to measure the ef-
fective acceleration 3 of the element 1. Here, the vessel has a
constriction causing the flow speed of the blood to temporarily
increase. Thus, the accelerometer 6 detects a temporary acceler-
ation (and deceleration in the widening region). Because the el-
ement 1 is passively carried in this example, the propulsion
force is zero. Hence, the effective acceleration 3 can directly
be used to determine properties of the vessel V, in this case
the presence of a constriction.
Fig. 4 shows an element 1 carried by a liquid in a vessel V. For
clarity, none of the propulsion means are shown in this schemat-
ic depiction, but the person skilled in the art will understand
that any of the described ways of moving, steering, or guiding
the device could be employed in this embodiment. Here, an imag-
ing unit 7 having an X-ray imaging device is employed. The ele-
ment 1 is visible in X-ray imaging. In addition, the blood con-
tains a contrast agent such that the vessel system is also visi-
ble under X-rays. A Doppler imaging unit 8 is employed to visu-
alize the flow 9 of the blood in the vessel system. Of course,
the Doppler imaging unit and the X-ray imaging device may be
connected to one computer each or to the same computer, for ex-
ample a computer comprising a computer program product according
to the invention for use of the imaging results in the calcula-
tion.
Fig. 5 shows an element 1 moving in a vessel V. Here, several
detectors 10 are placed around the vessel V. They are formed by
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closed copper coils around the vessel. The element comprises a
permanent magnet that creates a magnetic field around it. Thus,
when the element 1 passes a detector 10, the moving magnetic
field induces a current in the detector that can be detected. It
5 is also possible to provide an emitting chip on the robot and receiv-
ers/detectors placed on the body, that can triangulate the robot posi-
tion.
Fig. 6 shows another application of the method. Here, the ele-
10 ment is moving in a vessel and is propelled by a magnetic field
that exerts a force 2 on the element 1 via a ferromagnetic ele-
ment comprised in it. However, a blood clot C has formed in the
vessel V and blocks or restricts the blood flow. Consequently,
the element 1 stops moving as well once it hits the blood clot
15 C. Thus, the effective velocity of the element becomes zero,
while the propulsion force 2 is non-zero. This allows for the
determination of a property, in this case the presence of a
blood clot. Of course, it would also be conceivable to addition-
ally measure the effective acceleration of the element 1 which
would additionally give information about the location of the
blood clot C and/or its mechanical properties (a softer clot C
would lead to lower negative acceleration values).
Fig. 7 shows schematically a system according to the invention.
It comprises an element 1, in which a sensor 6 is arranged. The
sensor shown here is adapted to measure acceleration of the ele-
ment and, optionally, basic values such as temperature and pres-
sure. The system further comprises a measurement unit 11 and an
analyser unit 12. The measurement unit is in particular adapted
to receive acceleration values from the sensor. However, it may
also measure values based on markers or detectors 10. Although
not required to perform the method, in certain embodiments it
may be advantageous to measure the effective propulsion force
acting on the element 1. Thus, in this non-limiting example, the
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measurement unit 11 is also adapted to measure a magnetic field
at the location of the element, in particular by interaction
with the sensor 6. The analyser unit 12 is adapted to process
the values received from and by the measurement unit 11. In ad-
dition, it comprises a memory 15 to save values. For example, it
may receive an effective acceleration value from the sensor 6
comprised in the element 1. In addition, the propulsion force
may be known from the parameters of an external magnetic unit
(see Fig. 8) or be measured by the sensor 6. In any case, the
analyser unit is adapted to process these values and analyze
them to determine at least one property of the vessel. The prop-
erty value can optionally be saved in the memory 15. It would be
conceivable to combine the system with a display adapted to show
data, in particular two-dimensional and/or three-dimensional il-
lustrations of data such as a reconstruction of the anatomy of a
patient, based on the values saved in the memory. It will be un-
derstood that any of the examples and embodiments described
herein may be realized with this system.
Fig. 8 shows a magnetic element 14 that may be used to propel
the element 1. Here, it comprises an electromagnet that can se-
lectively be turned on and off to create a magnetic field 14. Of
course, a permanent magnet may also be employed. It would also
be conceivable to use electric energy to operate an impeller, a
propeller, or another propulsion means.
